One of the uses of photography has always been to capture the actual scene before the photographer in an image that is at least as good as that seen by the human eye. In some senses, the image may even be better than that seen by the human eye. Historically, the images have been captured as analog data. More recently, the images have been captured as digital data. Since digital images are the relative newcomer to the scene, they are compared to analog images as the standard for image capture. One of the most common complaints about digital image quality is poor highlight rendition by comparison to analog images. Scenes with a broad range of brightness levels may create artifacts in the image where the brightness level is too high for the saturation exposure level. The nature of the artifact is a “flat” highlight area. Depending on the size and location of the artifact, it may be noticeable to the human viewer. One response of the photographer might be to reduce the exposure level, but this may result is loss of detail in the lowest brightness level areas, or “shadows” regions, of the scene. Such a result may be undesirable.
In principal, these artifacts can be at least reduced by increasing the dynamic range of the image sensor so that the exposure can be reduced without increasing noise in the sensor. However, this requires lowering the noise floor of the sensor which is difficult if not impossible. Another approach to reduce or eliminate the artifacts is to compress the high brightness areas of the image so that detail can be rendered in the highlights without affecting the exposure level of the rest of the image. The latter is accomplished by utilizing at least two different saturation exposure levels. The higher saturation exposure level is used to render the higher brightness areas of the image and the lower saturation exposure level is used to render the lower brightness areas of the image. Conventionally, when one utilizes a single sensor array this has been accomplished in one of two ways. The first way is through the use of a dual element sensor array with some elements of the sensors having a higher saturation exposure level and the rest of the elements having a lower saturation exposure level. The drawback to the dual element sensor array is that the overall resolution is reduced because there are fewer elements of either saturation exposure level. The second way is through the use of a sequential images with one image having a higher exposure level and the other image having a lower exposure level. The drawback to the sequential image approach is that there is a time gap between the images. If the scene is moving, then there might be a scene change between images resulting in an artifact in the area of the movement.